This invention relates generally to flat panel display devices and particularly to an evacuatable envelope for such a device.
U.S. Pat. No. 4,145,633 discloses a flat panel display device in which the envelope includes a faceplate and a baseplate held in spaced parallel relationship by sidewalls. A plurality of support walls divide the envelope into a plurality of channels and support the faceplate and baseplate against collapse from atmospheric pressure. The faceplate supports a display screen which gives a visual output when struck by electrons. When a color display is desired shadow mask sections are arranged along the faceplate. The baseplate supports beam guide assemblies and other components required from the production of the visual display.
The display device is a cathode luminescent display and thus must be evacuated for proper operation. The sidewalls, therefore, must be permanently and hermetically affixed to the faceplate and baseplate. Typically, the faceplate, baseplate and sidewalls are made of glass and thus the hermetic seal is accomplished by fritting the sidewalls to the faceplate and baseplate. The frit seals are permanent and, therefore, the internal components must be present in the envelope during the fritting, resulting in several severe problems. High temperature and exposure to air of the internal components are required for the fritting. The beam guide meshes and shadow mask sections typically are thin metallic members and, therefore, corrode and frequently warp resulting in a high rejection rate. Additionally, upon evacuation the envelope is subjected to a high deformation force by atmospheric pressure. Because the faceplate must be made of glass and the baseplate and sidewalls typically are made of glass, the deformation must be minimal in order to prevent cracking. The support walls and sidewalls, therefore, must be dimensioned to tolerances within the permissible deformation of the faceplate and baseplate. The support and sidewalls can be made to the required tolerance by expensive existing techniques, but difficulties nevertheless arise. The frit cycle changes the dimensions of the sidewalls in an unpredictable manner so that even though the required tolerances are maintained while making the sidewalls and support walls, the fritting frequently causes the sidewalls to fall outside of the permissibly tolerances. Accordingly, when an assembled envelope is evacuated, this unpredictable difference can cause either the baseplate or the faceplate to crack.
The instant invention is directed toward an envelope for a flat panel display device which overcomes these difficulties.